Pirelli has played down concerns that the tyre issues Sebastian Vettel and Fernando Alonso had during second practice for the Belgian Grand Prix had anything to do with the blowouts seen at Silverstone earlier this year. Some drivers have asked for reassurances the tyres are safe, while Pirelli says the most like cause is some kind of debris on the track.

Vettel's tread came away from the shoulders of his right rear tyre, which Pirelli believes was caused by some debris getting caught between the floor of the car and tyre and rubbing against the tyre surface. Alonso's puncture was not caught on TV but resulted in two small holes through the tread of the tyre that caused it to deflate.

Pirelli will investigate what could have caused the punctures after finding cuts on tyres from other cars.

"It's a worry for the sport because we've got to go and find what it is," he said. "There is not a lot we can do. We will try our very best to identify it and give indications of what could be causing it."

Asked if there was any chance it was connected to the Silverstone blowouts, Hembery added: "It's completely different."

"It looks on the Red Bull like something has been rubbing on the surface and then cut through the surface," Hembery said. "It looks like something's got caught up between the floor and the tyre. On the Ferrari there are two quite clear holes through the top of the tread so we have got to go and look at the track later to see what's between turns 13 and 15.

"It could be anything. In the case of Alonso you have two holes through the top. What on earth could cause that? You've got to go and find it and that's what we've got to do."

Although Hembery said Pirelli had not experienced a similar problem at Spa-Francorchamps in previous years, he believes it is not that unusual for a grand prix weekend.

"It's the sort of thing you see through a weekend. We've seen some signs on other tyres as well - some surface cuts - so it's clearly something. I can't tell you what it is yet apart that it's from external sources."

Coming after the Silverstone blowouts, some drivers are keen to get reassurances the tyres will hold up, with Mark Webber telling BBC Sport: "We need answers. And 'debris' is not the answer."

However, Daniel Ricciardo said there had not been serious talks of a boycott in the drivers' briefing - a threat the drivers held over the sport after Silverstone.

"I'm not worried. It's not a concern," he said. "A few guys were obviously expressing a few of their concerns, but I'll let them sort it out. I think as a group if we have to try and decide something then, yeah, I'll have a voice, but for now I'm happy. I didn't have any problems today so I'm happy to keep going and try to make our car faster. That's our priority."

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